Liquid crystal display has number of advantageous such as low radiation, small volume and low power consumption, therefore widely used for products of notebook, PDA, flat television or mobile phone. The traditional liquid crystal display using outside driving chip to drive chip on the driver panel to display image. In order to reduce element numbers and decrease cost, the driving circuit structure directly be made on the display panel in recent years for example GOA technology, which integrates the grid driving circuit on glass substrate to form a scan driver on liquid crystal panel.
Comparing with traditional COF (Chip On Flex/Film) technology, the GOA technology could save a lot of manufacturing cost, and don't need bonging process of COF for Gate side, it helps enhancing yield. Therefore, GOA is a key technology of future development of liquid crystal panel.
Please refer to FIG. 1. The existing GOA circuit usually comprises multiple cascaded GOA units, each stage of the GOA unit is corresponding to a stage of a horizontal scan line. GOA unit comprises a pull-up control circuit {circle around (1)}, a pull-up circuit {circle around (2)}, a transmission circuit {circle around (3)}, a pull-down circuit {circle around (4)} and a pull-down holding circuit {circle around (5)}, and a bootstrap capacitor {circle around (6)} for enhancing potential. Wherein, the pull-up control circuit {circle around (1)} for controlling the turn-on time of the pull-up circuit {circle around (2)} to achieve precharging to the precharging signal Q(N), generally the previous-stage GOA unit transmits a transmission signal and a grid output signal; the pull-up circuit {circle around (2)} is for enhancing potential of the grid output signal G(N) and controls the turn-on of Gate; the transmission circuit {circle around (3)} is for controlling turn-on or turn-off signal of the GOA unit at next-stage; pull-down circuit {circle around (4)} is for pull-down the potential of Q(N), G(N) to VSS at first moment so that turn-off signal of G(N); the pull-down holding circuit {circle around (5)} is for holding potential of Q(N), G(N) to VSS, which is negative potential, usually there has two pull-down holding module are work alternatively; the bootstrap capacitor {circle around (6)} is for pull-up the Q(N) on second times, and its helpful output the G(N) of pull-up circuit.
The electric element of the pull-down holding circuit {circle around (5)} is an inverter, which could be Dariington structure inverter. The single stage GOA unit of the FIG. 1 could alternative to a single stage GOA unit of the FIG. 2. Please refer to FIG. 2, usually two of the pull-down holding circuits {circle around (5)} are alternatively work to prevent TFT T32, T42, T33, T43 be Positive Bias Stress(PBS) for long-time and made the threshold voltage Vth of element be forward deflection and cause the circuit failure.
However, two of the pull-down holding circuits {circle around (5)} are a reverse signal LC 1 and reverse signal LC2 respectively, which is the potential of LC 1 and LC 2 are difference at the same moment. When the LC1 is a high potential, the pull-down holding circuit {circle around (5)} positioned on left side of single-stage GOS unit is work for made the grid connected circuit point P(N) of TFT T42 and T32 stay in high potential status for a long time, such that the threshold voltage Vth of TFT T42 and T32 have forward deflection; Similarly, after a period of time, potential of LC1 and LC2 are alternative, the pull-down holding circuit {circle around (5)} positioned on right side of single-stage GOS unit is work for made the grid connected circuit point K(N) of TFT T43 and T33 stay in high potential status for a long time, such that the threshold voltage Vth of TFT T43 and T33 have forward deflection. If repeat it again and again with the long time using signal-stage GOA unit, forward deflection of the threshold voltage Vth of TFT T32, T42, T33 and T43 become more seriously, and causes entire GOA circuit failure.